Sandwich structures such as work station table tops generally include top and bottom facing sheets separated by a core made out of e.g., wood, particle board, or honeycomb material. Such table tops are used to provide a firm stable surface on which optical and other devices can be mounted or placed for scientific study or analysis.
To eliminate the effects of undesirable vibration, such sandwich structures are typically treated with a damping material. There are two prior art damping treatment methods: surface damping treatment and internal damping treatment.
In surface damping treatment methods, a damping layer is applied to one exterior surface, usually the bottom facing sheet, of the sandwich structure. Surface damping treatments are attractive because the damping layer applied to the surface does not reduce the stiffness or strength of the core. However, a much more effective location for the damping layer from a damping standpoint is inside the core, near its neutral plane. Such an internally damped structure exhibits a resonant compliance (a measure of damping performance) many times lower than comparable surface treatments.
Unfortunately, however, internal damping treatments also place the relatively compliant damping layer in the primary structural load path of the core severely reducing the stiffness and strength of the core. Such a structure will deflect undesirably under a static load and will also creep as the damping material stretches over time. For many applications, static strength and creep are critical design parameters and the internal damping treatment method cannot be used as a viable vibration control strategy.
Thus, surface damping treatments must be used which, as discussed above, do not always maximize vibration attenuation.